/* Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.activiti.engine.impl.jobexecutor;

import org.activiti.engine.ActivitiOptimisticLockingException;
import org.activiti.engine.impl.interceptor.CommandExecutor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * @author Daniel Meyer
 */
public class AcquireJobsRunnableImpl implements AcquireJobsRunnable {

    private static Logger log = LoggerFactory.getLogger(AcquireJobsRunnableImpl.class);

    protected final JobExecutor jobExecutor;
    protected final Object MONITOR = new Object();
    protected final AtomicBoolean isWaiting = new AtomicBoolean(false);
    protected volatile boolean isInterrupted = false;
    protected volatile boolean isJobAdded = false;
    protected long millisToWait = 0;

    public AcquireJobsRunnableImpl(JobExecutor jobExecutor) {
        this.jobExecutor = jobExecutor;
    }

    public synchronized void run() {
        log.info("{} starting to acquire jobs", jobExecutor.getName());

        final CommandExecutor commandExecutor = jobExecutor.getCommandExecutor();

        while (!isInterrupted) {
            isJobAdded = false;
            int maxJobsPerAcquisition = jobExecutor.getMaxJobsPerAcquisition();

            try {
                AcquiredJobs acquiredJobs = commandExecutor.execute(jobExecutor.getAcquireJobsCmd());

                for (List<String> jobIds : acquiredJobs.getJobIdBatches()) {
                    jobExecutor.executeJobs(jobIds);
                }

                // if all jobs were executed
                millisToWait = jobExecutor.getWaitTimeInMillis();
                int jobsAcquired = acquiredJobs.getJobIdBatches().size();
                if (jobsAcquired >= maxJobsPerAcquisition) {
                    millisToWait = 0;
                }

            } catch (ActivitiOptimisticLockingException optimisticLockingException) {
                // See https://activiti.atlassian.net/browse/ACT-1390
                if (log.isDebugEnabled()) {
                    log.debug("Optimistic locking exception during job acquisition. If you have multiple job executors running against the same database, " +
                            "this exception means that this thread tried to acquire a job, which already was acquired by another job executor acquisition thread." +
                            "This is expected behavior in a clustered environment. " +
                            "You can ignore this message if you indeed have multiple job executor acquisition threads running against the same database. " +
                            "Exception message: {}", optimisticLockingException.getMessage());
                }
            } catch (Throwable e) {
                log.error("exception during job acquisition: {}", e.getMessage(), e);
                millisToWait = jobExecutor.getWaitTimeInMillis();
            }

            if ((millisToWait > 0) && (!isJobAdded)) {
                try {
                    if (log.isDebugEnabled()) {
                        log.debug("job acquisition thread sleeping for {} millis", millisToWait);
                    }
                    synchronized (MONITOR) {
                        if (!isInterrupted) {
                            isWaiting.set(true);
                            MONITOR.wait(millisToWait);
                        }
                    }

                    if (log.isDebugEnabled()) {
                        log.debug("job acquisition thread woke up");
                    }
                } catch (InterruptedException e) {
                    if (log.isDebugEnabled()) {
                        log.debug("job acquisition wait interrupted");
                    }
                } finally {
                    isWaiting.set(false);
                }
            }
        }

        log.info("{} stopped job acquisition", jobExecutor.getName());
    }

    public void stop() {
        synchronized (MONITOR) {
            isInterrupted = true;
            if (isWaiting.compareAndSet(true, false)) {
                MONITOR.notifyAll();
            }
        }
    }

    public void jobWasAdded() {
        isJobAdded = true;
        if (isWaiting.compareAndSet(true, false)) {
            // ensures we only notify once
            // I am OK with the race condition
            synchronized (MONITOR) {
                MONITOR.notifyAll();
            }
        }
    }


    public long getMillisToWait() {
        return millisToWait;
    }

    public void setMillisToWait(long millisToWait) {
        this.millisToWait = millisToWait;
    }
}
